The general physical mechanics of the middle ear are well understood; many details, however, are still in the field of speculation; this also applies to the function of the tympanic membrane. Apart from the protection it offers against infection of the middle ear from the outside, the tympanic membrane appears to serve two purposes. One is the transfer of sound energy to the ossicular chain as an important part of the so-called transformer action of the middle ear, so that as little energy as possible is lost because of the difference of impedances between air and a fluid medium. The other purpose is the protection of the round window against sound energy, or at least to accomplish a phase difference between the energy that meets the oval and the round windows of the labyrinth.
According to current viewpoints (Békésy 1941, 1951) the eardrum can be thought of as a piston
TERKILDSEN K. Conduction of Sound in the Human Middle Ear. Arch Otolaryngol. 1961;73(1):69–79. doi:10.1001/archotol.1961.00740020073009
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